There is a growing interest in the use of artificial materials in clinical practice where these materials are in continuous contact with blood. Medical devices made from these materials are required to perform in the harsh biological environment in a specific application, for a specific duration without stimulating a biological response which may prove to be detrimental. Hence, such devices are required to be accepted by the biological environment for a specific application and duration, ie need to be bioacceptable. Improvements in bioacceptability are highly desirable for medical devices manufactured from artificial materials. Such materials commonly include polyvinyl chloride, polyethylene, polypropylene, polyurethanes, polycarbonates, stainless steel, silicones and the like. The biological response to blood contact with an artificial surface can be regarded in terms of different contributions from protein, platelet and blood cell deposition, together with platelet and blood activation leading to thrombus formation.
Many investigations have been carried out to prevent an artificial surface from provoking thrombus formation, ie to form a bioacceptable surface. Such investigations include the use of polymers which are natural, hydrophilic, hydrophobic, zwitterionic and charged (anionic and cationic). These types of polymers are non-thrombogenic, have had limited success and therefore application. Surface modification of an artificial material by heparin (ie formation of an anti-thrombogenic surface) has also proved to be intractable. Although clot formation has been reduced, platelet activation and blood cell activation are however still prevalent. Similarly, a particular artificial surface may be resistant to protein, platelet and blood cell deposition but may still activate blood constituents.
Each surface, whether non-thrombogenic or anti-thrombogenic, has its own profile of desirable bioacceptable properties, but no particular material possesses the full spectrum of the desired properties.
Additional disadvantages of some of the known approaches are (i) the procedures used to produce these materials are complex, (ii) the methods of applying these materials to the medical device are elaborate, and (iii) these processes utilise reagents which are highly toxic, even in minute quantities.
In a new approach to the problem of finding suitable bioacceptable materials, we have synthesised a novel non-thrombogenic polymer, and have also modified non-thrombogenic polymers by incorporating a polymerisable anti-thrombogenic compound, exemplified by polymerisable heparin. It was found that heparin activity was maintained, while the non-thrombogenity of the polymer component was prevalent. Other known biologically active anti-thrombogenic compounds include hirudin, warfarin and hyaluronic acid, and can be used in the same manner as the polymerisable heparin.